1. Field of the Invention
The invention relates to a modular connection of fuel cell stacks, more specifically to stack modules with a serial connection of the cathode gas inlets and outlets, more specifically to stack modules each having one inlet and one outlet common cathode gas side manifold for all the fuel cells in a module, in particular for Solid Oxide Fuel Cell (SOFC) stacks.
2. Description of the Related Art
The electro-chemical reactions and the function of a fuel cell is not the essence of the present invention, thus this is not explained in greater detail here, but considered known to a person skilled in the art.
To increase the voltage produced by the SOFC, several cell units are assembled to form a stack and are linked together by interconnects. These layers of the stack are sealed together by means of a gas tight and temperature resistant seal, such as glass, along some or all edges. There is a feasible limit to the size of stacks, to the area of each cell as well as to the number of cells which are assembled. The failure risk of a fuel cell stack increases with the number of cells and the size of the area. To increase the effect produced by SOFC it is therefore known to connect several stacks instead of simply increasing the cell area and number of cells in a single stack. The stacks can be connected in series and in parallel both on the electrical side and on the anode gas and cathode gas side of the stacks.
US 2006/0172176 A1 and U.S. Pat. No. 6,033,794 disclose examples of serially connected fuel cell stacks, but not how to realize the connection. U.S. Pat. No. 6,403,247 describes fuel cell stacks sharing a common gas input chamber, but a not serial connection where a common chamber connects the outlet of one stack or stack assembly to the inlet of another.
In spite of the presented known solutions to the connection problem of several fuel cell stacks, all of them have some of the inherent problems:                Though several stacks are connected in single modules, still the cathode gas manifolding has not been equally simplified.        When several stacks or several modules are connected in series, an extensive channelling/piping is necessary to connect to cathode and anode gas.        Connecting several stacks to increase effect also increases the supply system demand (heat exchangers for cooling and pre-heating).        Relative high temperature fuel cells, such as Solid Oxide Fuel Cell stacks has relative long start-up and shut-down periods.        SOFC assemblies of several stacks with relative large effect output, have a low flexibility towards varying the effect output.        